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The Sky This Week, 2016 November 29 - December 6

Signs of winter.
OrionRising01small.jpg
Orion rising, viewed from Blue Ridge Regional Park,
near Bluemont, Virginia, November 2004

The Moon returns to the evening sky this week, waxing through the crescent phases as she climbs through the southwestern sky. First Quarter occurs on the 7th at 4:03 am Eastern Standard Time. Look for Luna near the bright planet Venus on the evenings of the 2nd and 3rd. She passes ruddy Mars on the evenings of the 4th and 5th.

As November rolls into December we find ourselves experiencing the longest nights of the year here in the Northern Hemisphere. Even though the winter solstice doesn’t occur until the 21st, this week marks the beginning of a month-long period of solstice–related phenomena. From December 1st to the 11th we will see our earliest sunsets for the year. Here in Washington that time is 4:46 pm EST. However, the solstice itself doesn’t occur until the 21st, while the latest sunrise won’t occur until early January. Why the discrepancy? If we actually kept apparent solar time (like the time recorded by sundials), latest sunrise and earliest sunrises would indeed coincide with the solstice. However, the length of day as measured by the successive noon transits of the Sun is actually a bit longer than 24 hours at this time of the year. This is a result of Earth’s faster orbital motion as it nears perihelion, which occurs shortly after the start of the new year. The civil time that we observe is based on a "mean Sun" time that gives us a day that’s exactly 24 hours long. The difference between "apparent Sun" and "mean Sun" means that the extremes of sunrise and sunset don’t coincide with the solstice, but the length of day on the winter solstice is still the shortest for the year. The solstice "season" lasts about a month in December, and similar effects take place in June but only over a two-week interval. You can measure this for yourself. Old Sol will set about five minutes later than he does this week by the time the solstice rolls around. By the end of the month he sets 10 minutes earlier.

Another sure sign of the coming of winter is the rising of the bright stars that surround the constellation of Orion, the Hunter. By 10:00 pm the eastern sky is full of bright stars that surround the distinctive outline of Orion. The Hunter’s most prominent feature is the three bright stars that form his distinctive "belt". Follow an imaginary line toward the zenith ad the stars will point you toward the orange-tinted star Aldebaran in the constellation of Taurus, the Bull. Follow a similar line toward the horizon and you’ll spy the brightest star in the sky, Sirius, cresting the horizon. This star is usually and icy-blue beacon, but when it is close to the horizon it can seem to flicker through all the colors of the rainbow. Orion himself sports mostly blue stars, the exception being the ruddy-hued Betelgeuse. The star’s unusual name is a Latinized version of the ancient Arabic name "Ibt al Jauzah", which loosely translates as "The armpit of the mighty one".

In the early evening sky you’ll find Venus dominating the southwestern sky, popping out of the twilight shortly after sunset. She will be well-placed for photo opportunities on the 2nd and the 3rd when he hosts the waxing crescent Moon. She moves from Sagittarius into Capricornus by the end of the week.

Mars also receives a visit from the Moon on the evenings of the 4th and 5th. He is also trekking across the stars of Capricornus, keeping a nearly constant distance ahead of the Sun. When the Moon isn’t in the area you’ll find him as a solitary reddish beacon in a very barren stretch of the sky.

You’ll find Jupiter high in the east as morning twilight begins to gather. He is slowly drifting through the rising stars of Virgo, not far from the bright star Spica. He’s well-placed for an early-morning peek through the telescope.

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